Field of the Invention
The present invention relates to methods for maintaining or enhancing sperm motility, counteracting the effects of aging and exposure to environmental factors that can reduce sperm motility, and providing a more friendly environment in the womb or in vitro and in turn increase the likelihood of fertilization of oocytes through vaginal or in vitro insemination. It also relates to preservation of mammalian sperm for human and animal insemination, for example in livestock breeding.
Description of the Related Art
Sperm motility is a crucial factor for successful fertilization of oocytes (i.e., conception). The composition of the plasma membrane of the sperm is one the factors influencing sperm motility. The effects of aging, exposure to oxidative entities and changes in membrane lipid composition are important factors affecting male fertility. It has also been shown that changes in sperm membrane lipid composition are important factors resulting in a reduction in motility and the likelihood of fertilization. Peroxidation of the membrane lipids is also an important factor affecting for sperm health in adult life and as an individual ages.
The sperm cell has a unique structure and function. The sperm cell is viable in a body different from its origin, namely a female body, and is capable of navigating through the vagina and uterus to fertilize an egg released from the ovaries. The plasma membrane of the sperm cell also has a lipid composition different from most other cell membranes. It contains high amounts of polyunsaturated fatty acids (PUFA), particularly diPUFA (phospholipids esterified with two PUFA). PUFA are known to contribute to membrane fluidity and flexibility. The specific membrane lipid composition of the sperm cell has been found to be important for specific sperm functions promoting the creation of microdomains with different fluidity, fusogenicity, and permeability characteristics required for the sperm to navigate to, and to penetrate and fuse with the oocyte.
Phospholipids are key constituents of the lipid fraction of the sperm cell membranes, with phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin being the major components. The lipid and fatty acid composition of sperm cells differ for different animals and different species as well as for fertile and subfertile population of the same species. Therefore, published data on non-human sperm viability may not be translatable to the performance or viability of human sperm.
It is known that cryopreservation can affect the sperm membrane of non-human sperm. Further, freezing and thawing results in lipid modifications and domains of the sperm head plasma membrane react differently to cryopreservation. Furthermore, some studies investigated the ability of sperm cells in boar and bull semen to take up lipid components or fatty acids from the surrounding environment during incubation in vitro.
(Vasquez and Roldan, 1997) and, furthermore, Buhr et al. (1999) suggested a link between successful cryopreservation of boar semen and a given mixture of lipids and fatty acids in the original diluent. Once again, a specific role for the lipids present in the diluent or exchanges with spermatozoa are indicated. The present data also indicate that there was not only an uptake of lipid by sperm cells but also that this uptake was related to the quality of fresh semen. Phospholipase activities may mediate this lipid metabolism, totally or in part (for review, see Roldan, 1998). Buhr et al. (1994) reported an increase in the content of phospholipids, and in particular of phosphatidylcholine, during the cryopreservation of boar spermatozoa in the presence of egg yolk. The exact role of yolk components has not yet been clarified. Phosphatidylcholine (also called lecithin) has been proposed as the protective component during freezing (Quinn et al., 1980) since it prevented ultrastructural damage and favoured the maintenance of motility and respiration (Simpson et al., 1987). In contrast, studies have shown that phosphatidylcholine had no effect on boar sperm damage (Purse) et al., 1973) and did not prevent motility loss during cold shock and storage at −58 C (Watson, 1981). Phosphatidylserine has also been proposed as a protective agent in the boar (Butler and Roberts, 1975; Foulkes, 1977). Cationic low density lipoprotein (LDL) of egg yolk, characterized by a specific lipid:protein ratio of 2.7, was found to be the most efficient in protecting bull spermatozoa against cold shock. The cationic protein moiety of the LDL complex bound strongly to the sperm plasma membrane, which is negatively charged, and the lipid moiety was responsible for the protective action.” (Vishwanath et al., 1992). “Changes In Sperm Quality And Lipid Composition During Cryopreservation Of Boar Semen” S Cerolini, A Maldjian, F Pizzi, T M Gliozzi—Reproduction, 2001—Soc Reprod Fertility.
The major problem associated with cryopreservation of sperm cells is the loss of viability as a result of the freezing and thawing process. Loss of viability is related to membrane leakiness which is induced by sperm phospholipids peroxidation.
Infertility issues impact approximately 15% of all couples trying-to-conceive. Male infertility is a contributing factor in about half of these cases and high concentrations of oxidative-stress-causing agents have been identified in 30-80% of infertile men. Studies on the delivery of vitamin supplements and amino acids show an enhancement of specific sperm parameters (count, morphology, motility). Some antioxidants such as these vitamin C, selenium, vitamin E, L carnitine, Vitamin A, zinc and grapeseed extract have been shown to promote healthy sperm count, sperm morphology, and sperm motility, while reducing oxidative damage from agents, free radicals, or biological interactions that causes oxidative stress. (Dawson E B et al. Effects of ascorbic acid on male fertility. Ann N Y Acad Sci 1987; 498: 312-23).